The invention seeks to fulfill a need for a more precise and practical thermal indicator for indicating temperatures encountered in deep wells, such as oil wells and geothermal wells.
More particularly, it is an object of the invention to provide a thermal indicator for this purpose which can precisely indicate both static and dynamic temperatures of drilling fluids while withstanding the rigors of the drilling operation and without necessitating interruption of the latter.
A further important object of the invention is to provide a minute thermal indicator which will not clog the small drilling fluid passages of deep well drill bits while circulating with the drilling fluid.
Another object is to provide an indicator which is comprised of materials which will precisely indicate temperatures encountered in a well over the full range of temperatures which are normally experienced.
Another object is to provide a thermal indicator whose buoyancy in drilling fluids can be adjusted to compensate for changes in the consistency of such fluids during drilling operations.
Another important object of the invention is to provide an indicator of the above-mentioned type which is adapted to carry a permanent indicator marking which will survive passage of the indicator with the drilling fluid through the well during drilling operations.
Still another important object is to provide a thermal indicator for wells which employs a meltable solid indicator component, usually a metal alloy in coacting relationship with a heat resistant indicator substance, such as a heat resisting paint.
Another object of the invention is to provide a thermal indicator of the type mentioned immediately above, in which a variety of meltable alloys can be employed to form the meltable component, so that the latter will experience a clear and definite phase change in an extremely narrow and well defined temperature range.
Another object of the invention is to provide a precision thermal indicator for wells which is comparatively easy to manufacture at reasonable cost.